The present invention relates to a rotor and adapter for a centrifugal separator which centrifuges a sample in a sample tube by rotatably driving a rotor loaded with the sample tube.
In a centrifugal separator of this type, a sample tube containing a sample to be centrifuged is loaded in a rotor attached to a centrifugal machine. The rotor is rotated for a necessary period of time with a rotational speed (centrifugal force) necessary for separating the sample, so that the sample is centrifuged. The sample tube (e.g., a centrifuge tube) for receiving the sample to be subjected to centrifugal action is placed under a high centrifugal force, and accordingly the liquid sample contained in the sample tube generates an internal pressure. To prevent the sample tube from bursting by the internal pressure, the sample tube is made of a material that can withstand a high centrifugal force. In general, for centrifugal action with a centrifugal force of 10,000 xg or more, a material that can withstand a high centrifugal force is used. This leads to a high cost.
In order to solve this problem, in recent years, a tissue culture tube (to be merely referred to as a conical tube hereinafter) made of, e.g., a plastic is used as an inexpensive sample tube. As this conical tube is a container originally developed for tissue culture, it has undergone sterilization which is necessary for biological operation. Accordingly, when the conical tube is to be used as a sample tube for centrifugal action, additional sterilization can be omitted. In view of this fact, conical tubes have been conveniently used as sample tubes for centrifugal action.
When centrifugal action is to be performed with the conical tube, the conical tube must be prevented from bursting by the internal pressure of the liquid sample in it which is generated by the centrifugal force. For this purpose, a high dimensional precision that allows substantially no gap between the conical tube and the storing hole of the rotor is required. For example, Japanese Utility Model Publication No. 5-15955 discloses a bucket for a centrifugal separator for a conical tube. The bucket disclosed in this reference is a bucket mainly for low-speed centrifugal action.
As a rotor for high-speed centrifugal action, one as shown in FIG. 7 is available. Referring to FIG. 7, a rotor 2A for a centrifugal separator which rotates at a high speed has a mortar-like recess 2a in its upper surface. A plurality of (four) blind storing holes 3 are formed in the outer peripheral portion of the upper surface of the rotor 2A at substantially equiangular intervals in the circumferential direction such that their upper portions are inwardly inclined at required angles with respect to an axis X of the rotor 2A. A sample tube (conical tube) 4 shown in FIG. 8 is to be inserted in each storing hole 3. The sample tube 4 is formed of a plastic tube 5 having a bottomed and slightly tapered substantially cylindrical shape with a conical bottom, and a screw cap (to be merely referred to as a cap hereinafter) 6 serving as a lid for closing the upper end opening of the tube 5. A liquid sample 7 is poured into the tube 5.
In the tube 5, a diameter D1 at the upper end is slightly larger than a diameter D2 at the lower end, so the diameter gradually, slightly decreases from the upper end toward the lower end. A diameter D3 of the cap 6 is larger than the diameter D1 of the tube 5 at the upper end. The tube 5 is formed with a high dimensional precision that allows substantially no gap between the inner wall of the storing hole 3 of the rotor 2A described above and the sample tube 4 stored in the storing hole 3. More specifically, the storing hole 3 is also formed such that its diameter at its open end is larger than its diameter at its deep end, so that the sample tube 4 can be stored in the storing hole 3 with no gap. A depth L2 of the storing hole 3 is smaller than a total length L1 of the tube 5 of the sample tube 4, so that the upper end of the sample tube 4 stored in the storing hole 3 and the cap 6 project from the storing hole 3.
A driving shaft 9 is rotated by a motor (not shown). A hub 10 is fitted on the upper end of the driving shaft 9. A center hole 11 is formed to extend through the center of the rotor 2A. When the hub 10 is engaged in the center hole 11 and a set screw 12 is screwed into a screw hole formed in the hub 10, the rotor 2A is fixed to the hub 10. The hub 10 has a plurality of drive pins 13 for transmitting the rotation of the driving shaft 9 to the rotor 2A.
In this arrangement, when centrifugal action is to be performed, the sample tube 4 containing the liquid sample 7 is inserted in the storing hole 3 of the rotor 2A. When a motor (not shown) is driven, the driving shaft 9 rotates, and this rotation is transmitted to the rotor 2A through the hub 10. Hence, the rotor 2A rotates at a high speed to apply a centrifugal force to the liquid sample 7 in the sample tube 4. Thus, a sample with a high density is moved outward in the radial direction of the rotor 2A, and a sample with a low density is moved inward in the radial direction of the rotor 2A, thus separating the liquid sample 7.
It is confirmed that when the rotor 2A is rotated at 11,000 rpm (about 10,000 xg) to 12,000 rpm (about 14,000 xg) by using a centrifugal separator 1A for a high speed process having this arrangement, the sample tube 4 does not burst.
FIGS. 9, 10A, and 10B show a conventional case wherein a sample tube 4A has a small diameter. In this case, the small-diameter sample tube 4A is stored in the storing hole 3 of the rotor 2A through an adapter 41, and centrifugal action is performed. As shown in FIG. 10A, a diameter D4 of a tube 5 of the sample tube 4A is smaller than the diameter D2 of the tube 5 of the sample tube 4 shown in FIG. 7 described above. When the small-diameter sample tube 4A is stored in the storing hole 3 of the rotor 2A, as the inner diameter of the storing hole 3 and the outer diameter of the tube 5 of the sample tube 4A are different, if centrifugal action is performed, the tube 5 may burst. To prevent this, the sample tube 4A is stored in the storing hole 3 through the adapter 41 as shown in FIG. 10B.
More specifically, the adapter 41 has a bottomed cylindrical shape, and has a tube holding hole 44 for holding the tube 5A of the sample tube 4A. A depth L3 of the tube holding hole 44 is slightly smaller than a total length L4 of the tube 5A of the sample tube 4A. Therefore, when the tube 5A of the sample tube 4A is inserted in the tube holding hole 44 of the adapter 41, the tube 5A fits in the tube holding hole 44 with substantially no gap, and the cap 6A of the sample tube 4A projects from the tube holding hole 44 of the adapter 41, as shown in FIG. 9. A total length L5 of the adapter 41 is larger than the depth L2 of the storing hole 3 of the rotor 2A. When the adapter 41 is inserted in the storing hole 3, its upper end projects from the storing hole 3, as shown in FIG. 9.
In the states as shown in FIGS. 7 and 9, the liquid samples 7 in the sample tubes 4, 4A are centrifuged by rotating the rotor 2A at 11,000 rpm (about 10,000 xg) to 12,000 rpm (about 14,000 xg). When centrifugal action is ended, the operator holds caps 6, 6A of the sample tubes 4, 4A and extracts the sample tubes 4, 4A from the storing holes 3 of the rotors 2A respectively.
In recent years, due to the development in genetic analysis and the like, demand has arisen for further increasing the speed of the rotors 2A so that the rotors 2A can be rotated at near 15,000 rpm (about 22,000 xg). Under such higher centrifugal force, the entire side walls of the tubes 5, 5A of the sample tubes 4, 4A which try to expand by the internal pressure generated by the centrifugal force applied to the liquid samples 7 are supported by the inner walls of the storing holes 3 of the rotors 2A, so that it can be prevented from bursting.
Even if a play is formed between the tubes 5, 5A and the storing holes 3, when water is poured between them, a centrifugal force acts on the poured water, and a water pressure is generated. The water pressure acts as a pressure against the internal pressure generated by the liquid samples 7 in the tubes 5, 5A. Hence, bursting of the tubes 5, 5A can be prevented.
When, however, extracting the sample tubes 4, 4A from the storing holes 3, the operator must hold the caps 6, 6A with his or her fingers. For this purpose, the caps 6, 6A project from the storing hole 3 or adapter 41. Accordingly, due to the centrifugal force acting on the caps 6, 6A, the caps 6, 6A may deform as indicated by an alternate long and two short dashed line in FIG. 7, and its neck may be flattened and, in a worst case, may be torn, be broken, and scatter.